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Carboniferous strata of Andean Bolivia undergo facies change from fluvioglacial and glacial beds in the southeast, through fluvial and lacustrine facies, to deltaic facies in the northwest near Lake Titicaca. The Permo-Carboniferous boundary is conformable in the Titicaca region, where lowermost Permian strata include a zone of dark petroliferous brackish-water shales and the first of a series of bentonite/tuff zones. The volcanogenic beds recur throughout the Wolfcampian sequence, which is dominated by carbonates. The highest definitely Permian strata north of Lake Titicaca are algal-laminated dolostones; the overlying gypsum may be either Permian or Triassic.
The Permo-Carboniferous includes a complete spectrum of lithofacies generally considered to be paleoclimatically significant: tillite, coal, limestone, redbeds, and evaporites. Considered within their stratigraphic framework, these lithofacies reveal a picture of climatic gradients in time and space. The presence of red pigmentation in tillite, the association of tillite and fluvioglacial and lacustrine strata, and the presence of coals demonstrate that the subantarctic Carboniferous climate was modified by humid-arid cycles. During the Permian, subtropical carbonates overlapped fluvioglacial strata; subsequently, evaporites were deposited. These relations suggest rapid deglaciation caused by climatic amelioration, as well as postulated displacement of the Gondwana supercontinent.
A persistently emergent Protocordilleran ridge formed the western margin of the Andean Carboniferous basins. Widespread submergence and onset of volcanism characterized the earliest Permian.
Certain paleoclimatic anomalies, involving steep climatic gradients, characterize Carboniferous facies in Chile and Antarctica. It is proposed that they may be caused by either the noncoincidence of paleomagnetic and paleorotational poles, or by large-scale translation of sedimentary facies now in orogenic belts; sea-floor spreading is a mechanism which can move such facies from their original latitude of deposition.
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